1. Field
This disclosure relates generally to microelectronic technology, and more specifically, to apparatus used for heat dissipation in a microelectronic package and methods of fabricating the same.
2. Background Information
Recently, there has been rapid development in microelectronic technology and, as a result, microelectronic components are becoming smaller and circuitry within microelectronic components is becoming increasingly dense. As the circuit density increases, heat generation typically increases as well. Thus, heat dissipation is becoming more critical as the technology develops.
Various techniques may typically be used to remove or dissipate heat generated by a microelectronic component, which may also be referred to as a microelectronic die. These techniques may include passive or active solutions. One such technique, which may be classified as a passive solution, involves the use of a mass of conductive material in thermal contact with a microelectronic die. This mass of conductive material may alternatively be referred to as a slug, heat spreader, or integrated heat spreader (IHS). One of the primary purposes of a heat spreader is to spread, or absorb and dissipate the heat generated by a microelectronic die. This may at least in part eliminate “hot spots” within the microelectronic die.
A heat spreader may achieve thermal contact with a microelectronic die by use of a thermally conductive material, such as a thermal interface material (TIM) disposed therebetween. Typical thermal interface materials may include, for example, thermally conductive gels, grease or solders. Heat spreaders are typically constructed of a thermally conductive material such as aluminum, electrolytically plated copper, copper alloy, or ceramic, for example.
Referring now to the figures, where like elements are recited with like designations, there is illustrated numerous embodiments of a microelectronic package. FIGS. 4 and 5 are alternative views of one example of a microelectronic package 200. As is well known, a microelectronic package may comprise at least one microelectronic die 206, coupled to a heat spreader and a substrate 202, such as a printed circuit board (PCB). Package 200 comprises a microelectronic die 206 (see FIG. 4), coupled to a substrate 202, which may also be referred to as a substrate carrier. Secondary electronic components such as capacitors (not shown) may be attached to the substrate 202 as well. Typically, the microelectronic die 206 is attached to one side of the substrate 202, and attachment may be by means of a plurality of solder balls or solder bump connections 210 (see FIG. 4), although alternative attachment methods exist. The package 200 further comprises a mass of thermally conductive material, or heat spreader 204. Heat spreader 204 may be formed out of a suitable conductive material such as copper, aluminum, or carbon composites, although alternative materials exist. In package 200, the heat spreader 204 is typically in thermal contact with the microelectronic die 206 by means of a thermal interface material 208 (see FIG. 4). A contiguous lip 212 may be formed on the heat spreader 204, and may span around the microelectronic die 206. This lip 212 may serve as an attachment point for the heat spreader 204 to attach to the substrate 202, as well as to provide structural support for the body of the heat spreader 204. Additionally, the heat spreader 204 may provide structural support for the entire package 200, and may, for example, reduce or prevent warpage of the substrate 202. However, this substantially contiguous lip 212 typically does not contribute significantly to heat dissipation, and may add weight and cost to a device package. Additionally, the processes used to manufacture the substantially contiguous lip 212 of a heat spreader 204 may result in a greater variation in flatness of the top side 205 of a heat spreader, which may affect thermal performance due at least in part to a reduced contact surface area between the top side 205 of the heat spreader and a secondary device such as a heat sink. Heat spreader 204 may be attached to substrate 202 by using solder, sealants, or other types of adhesive materials, shown generally by attachment material 214, although alternative attachment methods exist. Heat spreaders, such as heat spreader 204, are typically attached to the substrate 202 by using a sealant 214, which substantially fills the gap between the heat spreader 204 and the substrate 202, and forms a completely enclosed cavity. In operation, heat is typically conducted from the microelectronic die 206 through the thermal interface material 208 to the heat spreader 204 by heat conduction. A vent hole 218 (see FIG. 5) may be formed in the heat spreader, and may provide pressure relief inside the package. A heat sink, such as a folded fin or an extruded pin heat sink, for example (not shown) may be attached to the top side 205 of the heat spreader 204, and in operation, heat is transferred from the heat spreader 204 to the heat sink, and convective heat transfer primarily transfers heat from the heat sink to the surrounding air. Heat sinks are typically attached to a heat spreader 204 by use of an adhesive material, or a mechanical attachment mechanism. Thermal performance may be affected by the method used to attach a heat sink, and depending on which method of attachment is used, such methods may result in heat sinks having a reduced heat transfer capability.
Heat spreaders, such as the one shown in FIGS. 4 and 5, are typically formed from a series of stamping processes, in a multistage manufacturing environment. These stamping processes typically result in a relatively low yield range in the production of heat spreaders, due, at least in part, to the processes used for forming heat spreaders. Additionally, the processes may result in a significant variation in flatness of the top surface 205 of a heat spreader 204, which, as explained previously, may increase the resistance of the package and reduce thermal efficiency. Additionally, the processes as described may affect bond line thickness 207 (see FIG. 4). Bond line thickness 207, or BLT, as is well known, is the distance from the top of a microelectronic die 206 to the bottom of a heat spreader 204 in the assembled microelectronic package 200. In addition to controlling or maintaining a BLT, there is typically a need to control the height of a second level attachment such as a heat sink, which may be a heat sink such as the types previously described. A greater variation in flatness may make dimensional control of this second level attachment device difficult. This design may additionally result in more costly and/or less effective attachment techniques for both the attachment of the heat spreader 204 to substrate 202, or the attachment of one or more devices such as a heat sink to the heat spreader 204. A need exists for an improved heat spreader design, which addresses at least some of these manufacturing and thermal performance concerns.